Industrial turbines and steam turbines each include a casing and a rotor rotatably supported by the casing. The turbine has a structure in which rotor discs are installed in the rotor in multiple stages in a rotor axial direction and rotor blades are embedded respectively in multiple rotor blade grooves provided in a peripheral surface of each rotor disc.
Here, description is given of the rotor blade groove with reference to FIG. 9A which is a perspective view showing a main portion of the rotor disc in a conventional rotor blade support structure in an enlarged manner. As shown in FIG. 9A, a rotor blade groove 110 penetrating one end surface portion 101b and the other end surface portion (not illustrated) opposite to the one end surface portion 101b is provided in a peripheral surface of the rotor 101. The rotor blade groove 110 includes circumferential groove portions 112, 112 in a bottom portion 113 of the rotor blade groove 110. The circumferential groove portions 112, 112 have arc-shaped ends and extend in a rotor circumferential direction beyond a portion above the bottom portion 113.